1. Field of the Invention
Embodiments of the invention generally relate to an apparatus and method for processing a substrate. More particularly, the present invention relates to detecting and controlling edge bevel removal of a semiconductor substrate.
2. Description of the Related Art
In semiconductor device manufacturing, a multilayer pattern of conductive, semiconductive, and/or insulating materials is usually generated on a substrate. Multiple deposition processes, such as chemical vapor deposition (CVD), physical vapor deposition (PVD), electrochemical plating (ECP), electroless plating, and/other deposition processes, are generally conducted in a process series to generate the multiplayer pattern.
During a deposition process, a conductive material is deposited on a front surface of a substrate. However, the conductive material may also deposit on edges, and sides, i.e. bevel, of the substrate where no pattern is located. For a metal layer deposited by a PVD process, the bevel and edge region is usually thin and unevenly deposited; therefore, the metal has poor adhesion and becomes a source of particle contamination. Some materials, e.g. copper, may also migrate from the edge and bevel region to neighboring active regions, especially during an annealing step.
For a conductive layer deposited by an ECP process, an excess amount of deposition, typically referred to as an edge bead, is formed near the edge region because plating current density is higher near the edge than the remainder of the substrate surface. The edge bead is particularly undesirable. The edge bead may be pulled up and away from the edge of the substrate due to mechanical stress.
Typically, a planarization process, such as chemical mechanical polishing (CMP) or electro-chemical mechanical polishing (ECMP), is conducted after plating to remove excessive deposit and/or polish the substrate surface between individual layer deposition steps to provide a relatively flat surface for the next deposition. The edge bead is easily torn off from the substrate, damaging the adjacent portion of the substrate. The broken bead may cause further damage to the devices when it becomes loose. To control edge beads, and other unwanted deposition near the edge and bevel region, an edge bevel removal (EBR) process is generally performed after a deposition step.
An EBR process may be conducted in an EBR system which is configured to dispense an etchant on the perimeter or bevel of a substrate to remove unwanted metal deposited thereon. After an EBR process, a rinse cell is generally used to rinse the surface of the substrate (front and/or back) with a rinsing solution to remove any contaminants and/or residual chemicals therefrom. The rinse cells are generally configured to spin the substrate at a high rate of speed to spin off any remaining rinsing solution droplets adhering to the substrate surface. Once the remaining fluid droplets are spun off, the substrate is generally clean and dray, and therefore, ready for the next process, e.g. chemical mechanical polishing.
Generally, there are two primary types of EBR systems which operate to remove the over deposited conductive layers from the substrate: nozzle-type and capillary-type. A nozzle-type EBR system generally rotates a substrate below a nozzle that dispenses a metal removing solution onto the edge and possibly backside of the substrate to remove the edge bead and over-deposited metal layer. Details of an exemplary nozzle-type EBR system may be found in U.S. Pat. No. 6,516,815 granted to Joe Stevens et al, titled “Edge Bead Removal/Spin Rise Dry (EBR/SRD) Module”. A capillary-type EBR system generally floats a substrate immediately above a plastic capillary ring configured to direct a metal removing solution dispensing on the back side of the substrate around the bevel area proximate the edge bead.
Although both types of EBR systems are generally effective in removing the edge bead and over deposited metal layer from the substrate, both systems suffer from inherent disadvantages: for example, the EBR systems have difficulty accurately centering substrates for processing without bowing or even breaking the substrate. Processing an off-centered substrate may cause uneven bevel edge, too thin or too wide bevel edge, incomplete removal, and decrease of valuable surface.
FIGS. 1 and 2 schematically illustrate a sectional view and a top view of a nozzle-type EBR system 100 of prior art. The EBR system 100 comprises a chamber body 101 defining a processing volume 108. A substrate support member 105 is disposed in the processing volume 108. The substrate support member 105 is configured to rotate a substrate 102 about a rotating axis 121. A lifting assembly 107 having a plurality of lifting pins 106 is disposed in the processing volume 108. The lifting assembly 107 is configured to move up and down along the rotating axis 121 so that the lifting pins 106 may pick up the substrate 102 from the substrate support member 105 or drop off the substrate 102 onto the substrate support member 105.
A fluid dispensing assembly 110 is positioned above the substrate support member 105. Referring to FIG. 2, the fluid dispensing assembly 110 comprises a dispensing nozzle 109 mounted on a pivoting arm 112 configured to move the dispensing nozzle 109 across the processing volume 108. The pivoting arm 112 may be driven by a motor 111. A fluid supply channel 113 is connected to the dispensing nozzle 109 providing a processing fluid to the substrate 102. The dispensing nozzle 109 is pointed radially outward to prevent the processing fluid from flowing towards central part of the substrate 102.
The EBR system 100 is configured to remove deposited metal from an edge region 104 of the substrate 102. During process, the substrate 102 is first positioned on the lifting pins 106 while the lifting pins 106 are on the up position and the substrate support member 105 is on the down position. The substrate 102 is then picked up by the substrate support member 105 and rotates about the rotating axis 121. A processing fluid, e.g. an etchant, is dispensed onto the substrate 102 from the dispensing nozzle 109 while the substrate 102 is rotating. The rotating movement spins the processing fluid outwards so that the deposited metal on the edge region 104 of the substrate 102 is removed and deposited metal on a surface area 103 available for patterning (hereafter available surface area 103) remains intact. The size of the edge region 104 may be adjusted by pivoting the pivoting arm 112.
Ideally, the available surface area 103 is a circle centered at the rotating axis 121 and the edge region 104 is an outer band of the substrate 102. As feature size decreases, maximization of available surface area 103 on the substrate 102 becomes important. Improper or inaccurate substrate centering can substantially limit the available surface area. Centering the substrate 102 at the rotating axis 121 and positioning the dispensing nozzle 109 in an accurate location are crucial to get an even and accurate edge region 104. However, EBR systems similar to the EBR system 100 have difficulties centering the substrate to be processed and accurately positioning the dispensing nozzle. FIG. 2 illustrates an example of an off centered edge removal result: the substrate center 122 is offset from the rotating axis 121 and the edge region 104 has a varied width around the substrate 102. As a result, some of the available surface area may be etched off and some undesired edge bead may remain even after an edge removal process. This may not only decrease the available surface area but also cause damage in latter processing steps. Additionally, misprocessing due to too small or too large an edge region may occur because of drifting in the position of the dispensing nozzle. Furthermore, contaminations or incomplete removal may result particle 120 in the edge region 104 after the edge bevel removal process. The offset, variation of nozzle location, and particles may be detected by running an inspection a separated inspection station. However, separated inspection decreases system efficiency and increases cost of ownership.
Therefore, there exists a need for an apparatus and method for detecting substrate conditions during an edge bevel removing process.